Bitter medicines and foods could be made more palatable with the addition of a natural chemical which could make them taste sweeter.

The addition of the substance could make very bitter medicines, such as HIV drugs, taste nicer.

Researchers who identified it say it could also replace the sugar, salt and fat that has to be added to processed foods to improve the taste.

When taste receptors in the mouth recognise bitter chemical compounds such as narigen, which is found in grapefruit, caffeine and ibuprofen, they release a protein called gustducin.

It will be interesting to see how this new substance is used and how well consumers respond to foods containing it

Brigid McKevith, British Nutrition Foundation

This triggers a series of reactions which tell the brain the food is "bitter".

Researchers from the biotech company Linguagen, based in New York, tested a large number of chemical compounds to see if they could find which one blocked the release of gustducin.

Each compound was mixed with a dye and one of the components found in the mouth.

The dye turned blue when gustducin had been produced. But when it did not turn blue, the researchers assumed that compound was blocking the production of gustducin.

All the compounds seen to be effective were nucleotides, a family of molecules which include the building blocks for DNA and RNA.

All occur naturally and are already found in various foods.

Tests on mice showed they could not distinguish between plain water and a bitter solution which had compound added to it.

Researchers then tested the most promising compounds themselves, tasting coffee and grapefruit juice to which compounds had been added.

Stephen Gravina, who carried out the experiment, said the coffee tasted "milder, and more mellow".

Although the research team cannot conclusively say why the compounds take away the bitter taste, they believe they work by bonding to the mouth's bitter taste receptors, inhibiting the release of gustducin.

Bitter pills

Human taste buds are programmed to detect even small amounts of bitterness because it could signal a substance is poisonous.

But the Linguagen researchers say bad smells and sour tastes, which are communicated to the brain in different ways, would still warn us if food had gone off.

The company has already patented the family of gustducin blockers, and says major food and pharmaceutical companies have expressed interest in their findings.

Brigid McKevith, a nutrition scientist with the
British Nutrition Foundation, told BBC News Online: "I think the main use of these blockers is going to be for bitter tasting medicines which may be especially useful."

She added: "As far as masking the bitter taste of foods, many people probably enjoy the taste of coffee and grapefruit as they are. Will milder and more mellow coffee encourage some people to drink more?

"It will be interesting to see how this new substance is used and how well consumers respond to foods containing it. That will be the real test."